parallel.h

///////////////////////////////////////////////////////////////////////
// File:        parallel.h
// Description: Runs networks in parallel on the same input.
// Author:      Ray Smith
//
// (C) Copyright 2013, Google Inc.
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
// http://www.apache.org/licenses/LICENSE-2.0
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
///////////////////////////////////////////////////////////////////////

#ifndef TESSERACT_LSTM_PARALLEL_H_
#define TESSERACT_LSTM_PARALLEL_H_

#include "plumbing.h"

namespace tesseract {

// Runs multiple networks in parallel, interlacing their outputs.
class Parallel : public Plumbing {
public:
  // ni_ and no_ will be set by AddToStack.
  TESS_API
  Parallel(const char *name, NetworkType type);

  // Returns the shape output from the network given an input shape (which may
  // be partially unknown ie zero).
  StaticShape OutputShape(const StaticShape &input_shape) const override;

  std::string spec() const override {
    std::string spec;
    if (type_ == NT_PAR_2D_LSTM) {
      // We have 4 LSTMs operating in parallel here, so the size of each is
      // the number of outputs/4.
      spec += "L2xy" + std::to_string(no_ / 4);
    } else if (type_ == NT_PAR_RL_LSTM) {
      // We have 2 LSTMs operating in parallel here, so the size of each is
      // the number of outputs/2.
      if (stack_[0]->type() == NT_LSTM_SUMMARY) {
        spec += "Lbxs" + std::to_string(no_ / 2);
      } else {
        spec += "Lbx" + std::to_string(no_ / 2);
      }
    } else {
      if (type_ == NT_REPLICATED) {
        spec += "R" + std::to_string(stack_.size()) + "(" + stack_[0]->spec();
      } else {
        for (auto &it : stack_) {
          spec += it->spec();
        }
      }
      spec += ")";
    }
    return spec;
  }

  // Runs forward propagation of activations on the input line.
  // See Network for a detailed discussion of the arguments.
  void Forward(bool debug, const NetworkIO &input, const TransposedArray *input_transpose,
               NetworkScratch *scratch, NetworkIO *output) override;

  // Runs backward propagation of errors on the deltas line.
  // See Network for a detailed discussion of the arguments.
  bool Backward(bool debug, const NetworkIO &fwd_deltas, NetworkScratch *scratch,
                NetworkIO *back_deltas) override;

private:
  // If *this is a NT_REPLICATED, then it feeds a replicated network with
  // identical inputs, and it would be extremely wasteful for them to each
  // calculate and store the same transpose of the inputs, so Parallel does it
  // and passes a pointer to the replicated network, allowing it to use the
  // transpose on the next call to Backward.
  TransposedArray transposed_input_;
};

} // namespace tesseract.

#endif // TESSERACT_LSTM_PARALLEL_H_